/**
 * 计算直方图
 * split()：将图像分割成对应的通道
 * calcHist()：来计算图像数组的直方图
 * normalize()：对数组进行归一化
 */

#include <opencv2/highgui.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/imgproc.hpp>
#include <iostream>

using namespace std;
using namespace cv;

int main(int argc, char *argv[]) {
    //! [Load image]
    CommandLineParser parser(argc, argv, "{@input | lena.jpg | input image}");
    Mat src = imread(samples::findFile(parser.get<String>("@input")), IMREAD_COLOR);
    if (src.empty()) {
        return EXIT_FAILURE;
    }
    //! [Load image]

    //! [Separate the image in 3 places ( B, G and R )]
    vector<Mat> bgr_planes;
    split(src, bgr_planes);
    //! [Separate the image in 3 places ( B, G and R )]

    //! [Establish the number of bins]
    int histSize = 256;
    //! [Establish the number of bins]

    //! [Set the ranges ( for B,G,R) )]
    float range[] = {0, 256}; //the upper boundary is exclusive
    const float *histRange = {range};
    //! [Set the ranges ( for B,G,R) )]

    //! [Set histogram param]
    bool uniform = true, accumulate = false;
    //! [Set histogram param]

    //! [Compute the histograms]
    Mat b_hist, g_hist, r_hist;
    calcHist(&bgr_planes[0], 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate);
    calcHist(&bgr_planes[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRange, uniform, accumulate);
    calcHist(&bgr_planes[2], 1, 0, Mat(), r_hist, 1, &histSize, &histRange, uniform, accumulate);
    //! [Compute the histograms]

    //! [Draw the histograms for B, G and R]
    int hist_w = 512, hist_h = 400;
    int bin_w = cvRound((double) hist_w / histSize);

    Mat histImage(hist_h, hist_w, CV_8UC3, Scalar(0, 0, 0));
    //! [Draw the histograms for B, G and R]

    //! [Normalize the result to ( 0, histImage.rows )]
    normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
    normalize(g_hist, g_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
    normalize(r_hist, r_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
    //! [Normalize the result to ( 0, histImage.rows )]

    //! [Draw for each channel]
    for (int i = 1; i < histSize; i++) {
        line(histImage, Point(bin_w * (i - 1), hist_h - cvRound(b_hist.at<float>(i - 1))),
             Point(bin_w * (i), hist_h - cvRound(b_hist.at<float>(i))),
             Scalar(255, 0, 0), 2, 8, 0);
        line(histImage, Point(bin_w * (i - 1), hist_h - cvRound(g_hist.at<float>(i - 1))),
             Point(bin_w * (i), hist_h - cvRound(g_hist.at<float>(i))),
             Scalar(0, 255, 0), 2, 8, 0);
        line(histImage, Point(bin_w * (i - 1), hist_h - cvRound(r_hist.at<float>(i - 1))),
             Point(bin_w * (i), hist_h - cvRound(r_hist.at<float>(i))),
             Scalar(0, 0, 255), 2, 8, 0);
    }
    //! [Draw for each channel]

    //! [Display]
    imshow("Source image", src);
    imshow("calcHist Demo", histImage);
    waitKey();
    //! [Display]

    return EXIT_SUCCESS;
}
